This invention relates to coating of particles, and more particularly electrolytic plating of metals and alloys onto small electrically conductive particles.
It is known to coat particles by such techniques as sputtering, spraying, electroless (autocatalytic) plating, coating with metal organic resonates, and electrolytic plating.
Electrolytic plating of particles involves placing a cathode and an anode in an appropriate electrically conductive solution, placing electrically conductive particles in the solution and in electrical contact with the cathode, and causing an electrical current to pass from the cathode to the anode. The passage of the electrical current through the solution causes reduction of ions in the solution, which results in deposition of a coating material on the particles in electrical contact with the cathode.
One technique for electrolytic plating of particles is described in Lashmore et al., U.S. patent application Ser. No. 08/317,532, filed Oct. 4, 1994, now U.S. Pat. No. 5,603,815, the entire disclosure of which is hereby incorporated herein by reference. In this technique, a bed of particles are placed in a cathodic container that is vibrated during the plating process. The vibration of the container causes fluidized motion of the bed of particles while the particles remain in electrical contact with the cathode, which avoids agglomeration of the particles and thereby enables accurate control of the volume ratio of the coating material to particle material on each of the particles.
By selecting an appropriate volume ratio of coating material to particle material and controlling the ratio for each of the particles, it is possible to engineer the physical and mechanical properties of the composite particles and articles formed from the composite particles. This technique is described in detail in Beane et al., U.S. Pat. No. 5,453,293, the entire disclosure of which is hereby incorporated herein by reference.